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| <TITLE>equal()</TITLE> |
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| <H2>equal()</H2> |
| <P><B>Library:</B> <A HREF="2-9.html">Algorithms</A></P> |
| |
| <PRE><HR><B><I>Function</I></B><HR></PRE> |
| |
| <UL> |
| <LI><A HREF="#sec1">Local Index</A></LI> |
| <LI><A HREF="#sec2">Summary</A></LI> |
| <LI><A HREF="#sec3">Synopsis</A></LI> |
| <LI><A HREF="#sec4">Description</A></LI> |
| <LI><A HREF="#sec5">Complexity</A></LI> |
| <LI><A HREF="#sec6">Example</A></LI> |
| <LI><A HREF="#sec7">Standards Conformance</A></LI> |
| </UL> |
| <A NAME="sec1"><H3>Local Index</H3></A> |
| No Entries |
| <A NAME="sec2"><H3>Summary</H3></A> |
| <P>Algorithm that compares two ranges of values for equality</P> |
| <A NAME="sec3"><H3>Synopsis</H3></A> |
| |
| <PRE>#include <algorithm> |
| |
| namespace std { |
| template <class InputIterator1, class InputIterator2> |
| bool equal(InputIterator1 start1, InputIterator1 finish1, |
| InputIterator2 start2); |
| |
| template <class InputIterator1, class InputIterator2, |
| class BinaryPredicate> |
| bool equal(InputIterator1 start1, InputIterator1 finish1, |
| InputIterator2 start2, BinaryPredicate |
| binary_pred); |
| } |
| </PRE> |
| <A NAME="sec4"><H3>Description</H3></A> |
| <P>The <SAMP>equal()</SAMP> algorithm does a pairwise comparison of all of the elements in one range with all of the elements in another range to see if they match. The first version of <SAMP>equal()</SAMP> uses <SAMP>operator==()</SAMP> as the comparison function, and the second version allows you to specify a binary predicate as the comparison function. The first version returns <SAMP>true</SAMP> if all of the corresponding elements are equal to each other. The second version of <SAMP>equal()</SAMP> returns <SAMP>true</SAMP> if for each pair of elements in the two ranges, the result of applying the binary predicate is true. In other words, <SAMP>equal()</SAMP> returns <SAMP>true</SAMP> if both of the following are true:</P> |
| <UL> |
| <LI><P CLASS="LIST">There are at least as many elements in the second range as in the first</P></LI> |
| <LI><P CLASS="LIST">For every iterator <SAMP>i</SAMP> in the range <SAMP>[start1, finish1)</SAMP> the following corresponding conditions hold: </P></LI> |
| <P CLASS="LIST"><SAMP>*i == *(start2 + (i - start1))</SAMP></P> |
| <P CLASS="LIST">or</P> |
| <P CLASS="LIST"><SAMP>binary_pred(*i, *(start2 + (i - start1))) == true</SAMP></P> |
| </UL> |
| <P>If one of these conditions is not true, <SAMP>equal()</SAMP> returns <SAMP>false</SAMP>.</P> |
| <P>This algorithm assumes that all iterators in the range <SAMP>[start2, start2 + (finish1 - start1)]</SAMP> are dereferenceable.</P> |
| <A NAME="sec5"><H3>Complexity</H3></A> |
| <P><SAMP>equal()</SAMP> performs at most <SAMP>finish1 - start1</SAMP> comparisons or applications of the predicate.</P> |
| <A NAME="sec6"><H3>Example</H3></A> |
| |
| <UL><PRE>// |
| // equal.cpp |
| // |
| |
| #include <algorithm> // equal |
| #include <functional> |
| #include <iostream> |
| #include <vector> |
| |
| |
| |
| int main () |
| { |
| // Typedef for convenience. |
| typedef std::vector<int, std::allocator<int> > vector; |
| |
| typedef std::ostream_iterator <vector::value_type, char, |
| std::char_traits<char> > os_iter; |
| |
| const vector::value_type a1[] = { 1, 2, 3, 4 }; |
| const vector::value_type a2[] = { 1, 2, 4, 3 }; |
| |
| // Set up two vectors. |
| const vector v1(a1, a1 + sizeof a1 / sizeof *a1); |
| const vector v2(a2, a2 + sizeof a2 / sizeof *a2); |
| |
| // Check for equality. |
| bool same = std::equal(v1.begin(), v1.end(), |
| v2.begin()); |
| |
| same = same && std::equal(v1.begin(), v1.end(), |
| v2.begin(), std::equal_to<vector::value_type>()); |
| |
| // Output the sequences. |
| std::cout << "{ "; |
| std::copy(v1.begin(), v1.end(), os_iter(std::cout, " ")); |
| |
| std::cout << "} == { "; |
| std::copy(v2.begin(), v2.end(), os_iter(std::cout, " ")); |
| |
| // Output the result. |
| std::cout << "} --> " << std::boolalpha |
| << same << std::endl; |
| |
| return 0; |
| } |
| |
| |
| Program Output |
| </PRE></UL> |
| <UL><PRE>{ 1 2 3 4 } == { 1 2 4 3 } --> false |
| |
| </PRE></UL> |
| <A NAME="sec7"><H3>Standards Conformance</H3></A> |
| <P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems --Programming Language C++, Section 25.1.8</I></P> |
| |
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